<!DOCTYPE html>
<!-- Any copyright is dedicated to the Public Domain.
   - http://creativecommons.org/publicdomain/zero/1.0/ -->

<html>
  <style>
  div#details::first-line {
    color: blue;
  }
  </style>
  <body>
    <div id="details">
      <span>Summary
        <div>Block in summary</div>
      </span>
      <span>This is the details.</span>
    </div>
  </body>
</html>
